144 lines
11 KiB
HTML
144 lines
11 KiB
HTML
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<title>std::ranges::view_interface<D>::data</title>
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<body class="mediawiki ltr sitedir-ltr ns-0 ns-subject page-cpp_ranges_view_interface_data skin-cppreference2 action-view cpp-navbar">
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::ranges::view_interface<D>::</span>data</h1>
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<div id="bodyContent">
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<div id="contentSub"><span class="subpages">< <a href="cpp.html">cpp</a>‎ | <a href="cpp-ranges.html">ranges</a>‎ | <a href="cpp-ranges-view_interface.html">view interface</a></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">auto</span> data<span class="br0">(</span><span class="br0">)</span><br />
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requires std<span class="sy4">::</span><span class="me2">contiguous_iterator</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span>D<span class="sy1">>></span><span class="sy4">;</span></span></div>
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<td>(1)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw4">constexpr</span> <span class="kw4">bool</span> data<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><br />
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requires std<span class="sy4">::</span><span class="me2">contiguous_iterator</span><span class="sy1"><</span>ranges<span class="sy4">::</span><span class="me2">iterator_t</span><span class="sy1"><</span><span class="kw4">const</span> D<span class="sy1">>></span><span class="sy4">;</span></span></div>
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<td>(2)</td>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td>
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<p><code>data</code> 成员函数的默认实现经由 <span class="t-lc">std::to_address</span> 获得起始迭代器所代表的地址，在派生类型的视图非空时，它亦是视图所引用的连续存储（为 <a href="cpp-iterator-contiguous_iterator.html"><code>contiguous_iterator</code></a> 所蕴含）的最低地址。</p>
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<div class="t-li1"><span class="t-li">1)</span> 令 <code>derived</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span>D<span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span></span></span> 。等价于 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> std<span class="sy4">::</span><span class="me2">to_address</span><span class="br0">(</span>ranges<span class="sy4">::</span><span class="me2">begin</span><span class="br0">(</span>derived<span class="br0">)</span><span class="br0">)</span><span class="sy4">;</span></span></span> 。</div>
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<div class="t-li1"><span class="t-li">2)</span> 同 <span class="t-v">(1)</span> ，除了 <code>derived</code> 为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">static_cast</span><span class="sy1"><</span><span class="kw4">const</span> D<span class="sy3">&</span><span class="sy1">></span><span class="br0">(</span><span class="sy2">*</span>this<span class="br0">)</span></span></span> 。</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
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<p>（无）</p>
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<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
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<p>起始迭代器所代表的地址。</p>
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<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
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<p>下列派生类型可能使用 <code>data</code> 的默认实现：</p>
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<ul>
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<li><span class="t-lc">std::ranges::drop_view</span></li>
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<li><span class="t-lc">std::ranges::drop_while_view</span></li>
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<li><span class="t-lc">std::ranges::ref_view</span></li>
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<li><span class="t-lc">std::ranges::subrange</span></li>
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<li><span class="t-lc">std::ranges::take_view</span></li>
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<li><span class="t-lc">std::ranges::take_while_view</span></li>
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</ul>
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<p>下列类型派生自 <span class="t-lc">std::ranges::view_interface</span> 并且不声明其自身的 <code>data</code> 成员函数，但它们无法使用默认实现，因为其迭代器类型决不满足 <a href="cpp-iterator-contiguous_iterator.html"><code>contiguous_iterator</code></a> ：</p>
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<ul>
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<li><span class="t-lc">std::ranges::basic_istream_view</span></li>
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<li><span class="t-lc">std::ranges::common_view</span></li>
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<li><span class="t-lc">std::ranges::elements_view</span></li>
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<li><span class="t-lc">std::ranges::filter_view</span></li>
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<li><span class="t-lc">std::ranges::iota_view</span></li>
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<li><span class="t-lc">std::ranges::join_view</span></li>
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<li><span class="t-lc">std::ranges::reverse_view</span></li>
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<li><span class="t-lc">std::ranges::split_view</span></li>
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<li><span class="t-lc">std::ranges::transform_view</span></li>
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</ul>
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<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
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<div class="t-example">
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<div class="t-example-live-link"></div>
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<div class="cpp source-cpp">
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<pre class="de1"><span class="co2">#include <array></span>
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<span class="co2">#include <iostream></span>
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<span class="co2">#include <ranges></span>
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<span class="co2">#include <string_view></span>
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<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
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<span class="kw4">constexpr</span> <a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> str <span class="br0">{</span> <span class="st0">"Hello, C++20!"</span> <span class="br0">}</span><span class="sy4">;</span>
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<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1"><<</span> <span class="br0">(</span>str <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">drop</span><span class="br0">(</span><span class="nu0">7</span><span class="br0">)</span><span class="br0">)</span>.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span> <span class="sy1"><<</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">static</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a> a <span class="br0">{</span> <span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span> <span class="br0">}</span><span class="sy4">;</span>
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<span class="kw4">constexpr</span> <span class="kw4">auto</span> v <span class="br0">{</span> a <span class="sy3">|</span> std<span class="sy4">::</span><span class="me2">views</span><span class="sy4">::</span><span class="me2">take</span><span class="br0">(</span><span class="nu0">3</span><span class="br0">)</span> <span class="br0">}</span><span class="sy4">;</span>
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static_assert<span class="br0">(</span> <span class="sy3">&</span>a<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">==</span> v.<span class="me1">data</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">)</span><span class="sy4">;</span>
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<span class="br0">}</span></pre></div>
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</div>
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<p>输出：</p>
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<div dir="ltr" class="mw-geshi" style="text-align: left;">
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<div class="text source-text">
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<pre class="de1">C++20!</pre></div>
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</div>
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</div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
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<table class="t-dsc-begin">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-iterator-data.html"><span class="t-lines"><span>data</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx17">(C++17)</span></span></span></div>
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</div>
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</td>
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<td>获得指向底层数组的指针<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-data.html"><span class="t-lines"><span>ranges::data</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>获得指向连续范围的起始的指针<br />
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<span class="t-mark">(定制点对象)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-ranges-cdata.html"><span class="t-lines"><span>ranges::cdata</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>获得指向只读连续范围的起始的指针<br />
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<span class="t-mark">(定制点对象)</span></td>
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</tr>
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<tr class="t-dsc">
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<td>
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<div class="t-dsc-member-div">
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<div><a href="cpp-memory-to_address.html"><span class="t-lines"><span>to_address</span></span></a></div>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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</div>
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</td>
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<td>从指针式类型获得裸指针<br />
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<span class="t-mark">(函数模板)</span></td>
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</tr>
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</table>
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</div>
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<div class="visualClear"></div>
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</div>
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</body>
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